1. Field of the Invention
This invention relates generally to disks and disk drives, and more particularly to methods and apparatus for thermally bonding lubricant to a disk with use of a heat source at an air bearing surface (ABS) of a magnetic head.
2. Description of the Related Art
A write head is typically combined with a magnetoresistive (MR) or giant magnetoresistive (GMR) read head to form a magnetic recording head, certain elements of which are exposed at an air bearing surface (ABS). The write head comprises first and second pole pieces connected at a back gap that is recessed from the ABS. The first and second pole pieces terminate at the ABS where they define first and second pole tips, respectively. An insulation stack, which comprises a plurality of insulation layers, is sandwiched between the first and second pole pieces, and a coil layer is embedded in the insulation stack. A processing circuit is connected to the coil layer for conducting write current through the coil layer which, in turn, induces magnetic write fields in the first and second pole pieces.
A non-magnetic gap layer is sandwiched between the first and second pole tips. Write fields of the first and second pole tips at the ABS xe2x80x9cfringexe2x80x9d across the gap layer. In a magnetic disk drive, a magnetic disk is rotated adjacent to, and a short distance (fly height) from, the ABS so that the write fields magnetize the disk along circular tracks. The written circular tracks then contain information in the form of magnetized segments with fields detectable by the MR or GMR read head.
One or more heads may be employed in a magnetic disk drive for reading and writing information on circular tracks of a rotating disk. A magnetic recording head is mounted on a slider that is carried on a suspension. The suspension is mounted to an actuator which places the magnetic head to locations corresponding to desired tracks. As the disk rotates, an air layer (an xe2x80x9cair bearingxe2x80x9d) is generated between the rotating disk and an air bearing surface (ABS) of the slider. A force of the air bearing against the air bearing surface is opposed by an opposite loading force of the suspension, causing the magnetic head to be suspended a slight distance (i.e. its fly height) from the surface of the disk.
It is generally desirable to minimize the fly height of a magnetic head. With lower fly heights between the magnetic head and the disk, however, there is an increasing rate of intermittent contacts between the head and the disk. This may result in damage to the disk surface. To mitigate these problems, lubricants are often coated on the disk surface during manufacturing. After the disk surface is coated with the lubricant, it is typically heated in an oven to help xe2x80x9cbondxe2x80x9d the lubricant to the disk surface. This bond may be made through physical absorption such that the lubricant attaches to carbon on the disk surface. After this process, a large amount of the lubricant (e.g. close to 100%) may be bonded to the disk surface.
In time, however, some of the lubricant will debond from the disk surface depending on particular environmental conditions such as humidity. The debonding process creates what may be generally referred to as xe2x80x9cmobilexe2x80x9d lubricant. After such debonding, there may be between 20-50% mobile lubricant on the disk surface. Mobile lubricant is indeed mobile and moves across the disk surface, creating differences in lubricant thickness from the inner diameter (ID) to the outer diameter (OD) of the disk. In particular, air shear forces due to disk rotation and interaction with the slider push the mobile lubricant from the ID to the OD, creating a much thicker lubricant at the OD than the ID. Eventually, the excess mobile lubricant may be spun off of the disk surface and become too thin or depleted on the disk surface to be effective.
Thus, although the disk is coated and bonded with lubricant during manufacture to protect it from the intermittent contact with the head, the lubricant may be depleted from the disk surface during operation of the drive. Because of these problems, several types of lubricant reservoir systems have been disclosed as a means for continuously maintaining a lubricant film on the disk during operation. Use of such lubricant reservoirs, however, may provide too much mobile lubricant than needed. If the mobile lubricant becomes too thick on the disk surface, it may cause oscillating write errors or oscillating thermal erasures. If the excess mobile lubricant is spun off the disk surface, the lubricant may be picked up by the slider and there may be an undesirable slider-to-disk bridging.
Accordingly, what are needed are improved methods and apparatus for bonding lubricants to the surfaces of magnetic disks.
A method of bonding lubricant to a surface of a magnetic disk in a disk drive involves providing a heat source at an air bearing surface (ABS) of a magnetic head; causing the heat source to be energized to produce heat; and causing the magnetic head to be moved across a surface portion of a magnetic disk so that lubricant is thermally bonded to the surface portion from the heat provided by the heat source. Preferably, this lubricant bonding mode of operation of the disk drive is performed on a regular or periodic basis. Alternatively, the mode is activated based on a predetermined environmental condition (e.g. temperature or humidity) or an external signal.
In a first embodiment, the heat source is comprised of first and/or second pole pieces of the magnetic head through which an electrical current is passed. In a second embodiment, the heat source is comprised of a separate heating element which is formed on or within the magnetic head. In this second embodiment, the heating element may be the same heating element that is utilized for thermal-assist writing to the magnetic disk. In a third embodiment, heat is generated by reading data from a data block on the disk and writing the data back to the data block in a repetitive fashion.